SPOTLIGHT

Author Bio

Bob Wettermann is the president of BEST Inc., a contract rework and repair facility in Chicago. BEST develops processes and products for a variety of PCB and device rework challenges. Bob is an IPC Master Instructor and has been involved in the electronics assembly and repair market for more than 18 years. He holds several patents in the fields of surface science, industrial controls and PCB rework. He is a BSEE from the University of Illinois/Champaign.

Replating of Gold Fingers: Getting the Shine Back

There are several instances where the gold contacts on PCBs need to be replated. IPC A-610 discusses several of these cases. One of the more common defects is when solder "splashes" onto the contact during the wave or selective soldering process, thereby contaminating it. This requires that the operator strip away the solder, first by wicking off excess solder and then to a greater degree via mechanical and chemical stripping means. This is then followed by a replating of the contacts. Another defect is when "pitting" occurs in the contact area. This pitting is a result of a defective plating operation. Many times, this defect can be buffed out and then it can be replated. Other times, the contact area is scratched, which similarly requires the buffing out of the scratch followed by replating.

Gold replating of these contacts is a process that requires setup, special chemistry that requires advanced PCB repair tech skill, and the correct materials and training.

The operator skills required for gold contact replating are similar to those required for micro device rework and PCB repair. Patience, dexterity and the ability to improvise correctly if the standard process followed does not go as planned are all attributes of a PCB rework and repair technician. The most experienced and skilled techs are the right ones for being trained to perform PCB repair techniques such as gold finger replating.

Figure 1: Stripping the remnants as part of preparing the contacts for replating.

Numerous materials are required for the proper repair of gold fingers per the industry standard IPC-7721 4.6.3, which in many cases can be had in a complete replating kit. Several solutions are required for the replating process, including the gold stripping and the nickel and the gold plating solutions. Applicator tips are put onto the end of the electrodes and come in a variety of sizes to accommodate the different gold finger geometries. A variable power supply will supply the current for the plating process. In addition, there are polishing materials including the polishing compound and water to rinse the remnant compound off the board. Finally, a grounding wire is used to form the bus to all the contacts requiring replating. As a warning, the replating area should be properly ventilated and care must be taken for this process as the solutions are hazardous in nature.

Figure 2: Replating the contact with gold solution.

There are numerous ways personnel can be trained in this PCB repair procedure. One method is via the IPC-7721 PCB repair program. This industry certification program can accommodate the training of this repair technique at the CIS level. Otherwise various training companies or gold replating suppliers can provide training in this repair technique.

The basic replating process is referenced in IPC-7721 4.6.3 or in the manufacturer’s instructions as part of the gold replating kit. If the gold finger is severely damaged, a gold-plated circuit frame and the pad repair process as outlined in IPC-7721 procedure 4.6.1 or 4.6.2 can be utilized to replace the finger lieu of the replating process.

If you are outsourcing this as a service, inspect the replated area per the most recent IPC-A-610 guidelines (Revision G, Section 10.1.1). The bond strength of the plating material can also be measured using the peel tape test found in IPC TM-650.

2018

There are several instances where the gold contacts on PCBs need to be replated, and IPC A-610 discusses several of these cases. This column by Bob Wettermann discusses gold replating of defective contacts caused by processes such as wave or selective soldering, or plating.

Masking of printed circuit boards post rework/repair as well as for initial PCB assembly is often required if the PCB is to be conformal coated. If a board that has conformal coating on it needs to be reworked or repaired, the conformal coating needs to first be removed before the operation of rework or repair can take place. This article centers around the various options for conformal coating masking via a liquid application process.

"Dead bug" attachment of electronic components is a way of building functioning electronic circuits by soldering the parts directly together or by soldering miniature jumper wires between the component leads and the PCB lands instead of the traditional surface mount or through-hole soldering of components onto a PCB.

There are a variety of reasons behind pads getting "lifted" completely or partially from the laminate of a PCB. Per the just revised IPC-A-610 Revision G, a defect for all three classes occurs when the land is lifted up one or more pad thicknesses. Lifted pads can occur when a device has been improperly removed or there is a manufacturing defect in the board construction. In any case, as with any repair, the ultimate decision on the ability to repair the pad lies with the customer.